1. Field of the Invention
The disclosed embodiment relates to an antenna device and a radar device.
2. Description of the Related Art
Conventionally, an antenna device in which a plurality of microstrip antennas each configured with a set of radiating elements arranged in series on a feedline is arranged in parallel on a surface of a dielectric substrate is known (e.g., Japanese Patent Application Laid-open No. 8-167812).
Such antenna device is installed, for example, in an onboard radar device for a vehicle and used, for example, for a vehicle following function in which a vehicle running ahead of, and on the same lane as, the own vehicle is detected as a target and the own vehicle follows the vehicle running ahead.
Specifically, the antenna device disclosed in Japanese Patent Application Laid-open No. 8-167812 is equipped with an insulation plate layered on a portion of the dielectric substrate on which the feedline is formed so as to insulate the feedline from the space. Thereby, unwanted radiation of radio wave from the feedline and a feeder circuit including a radiating element is restrained.
However, there is still a room for improvement in the prior art described above to prevent a radio wave interference occurring between neighboring microstrip antennas.
For example, it is known that the radio wave propagates not only in a space but also in the dielectric substrate, an adhesive sheet for bonding the dielectric substrate to a housing which acts as a waveguide, or the like. Therefore, the prior art described above is insufficient for restraining such propagation and preventing radio wave interference.
The radio wave interference can be prevented by lengthening the distance between the neighboring microstrip antennas. However, the lengthening is not preferable because the device may fail to satisfy the required level of performance, and the space for arrangement become large.